How can I secure my notebook at public Wi-Fi hotspots

Because public hotspots generally does not use encryption, you should assume that anyone can see your Internet traffic, unless you take preventive measures.

Please make sure it is a legitimate hot spots: know evil type setting with a familiar SSID name, such as "Wayport" or "t-mobile," Pirates of the router, and then use them to capture the unsuspecting user login information and other personal data.
Verify that your PC software firewall is turned on, and Windows file sharing is turned off; it is closed by default in Windows XP Service Pack 2. To check this setting, open the control panel and selecting Windows Firewall (you may have to click the Security Center in XP or Vista for the first time). In XP, select the Exceptions tab, and view programs and services to ensure that the "file and printer sharing" is not selected. In Vista, click Change settings, and then select the Exceptions tab and follow the instructions XP.
Never send banking passwords, credit card numbers or other sensitive data, confidential e-mail messages unless you're sure you're on a secure Web site: see the lock icon in the lower right corner of your browser, and start with an HTTPs URL in the address bar. Such websites at their own encryption.
Always radio turn off when you're not in a Wi-Fi hotspot: hackers can use it to create an equivalent of the Wi-Fi connection with your computer and accessing it directly.
For better security, consider paid subscription to hotspot network as chirp or t-mobile contract. The two companies provide connection software that automatically encrypt your session.